In 1935, the U.S. Army dropped 40 bombs on Mauna Loa’s lava flow, setting off a volcanic experiment whose outcome is still debated over 90 years later. On December 27, 1935, U.S. military aircraft dropped 40 bombs on an active lava flow from Mauna Loa in Hawaiʻi. The operation targeted lava channels feeding a flow that was moving toward Hilo and the headwaters of the town’s water supply. Lava Channels Carried Molten Rock Toward HiloPāhoehoe is a type of basaltic lava with a smooth, billowy or rope-like surface. Later studies found that the 1935 bombing and another attempt in 1942 produced limited effects.